Power Supply; Fault Protection - Newport New Focus Picomotor 8743-CL User Manual

3.5

Power Supply

The 8743-CL Controller/Driver can place stress on the system power supply. The stress
has two components:
Inrush current: The inrush current on power-up charges the internal filter capacitor.
While the energy magnitude of the inrush current is limited, it can still cause problems
with power supplies not designed to handle it.
Dynamic load: Dynamic current is supplied to the 8743-CL internal power supply for
each Picomotor drive pulse. The input-filter capacitor will supply more dynamic current as
the resistance between the capacitor and system power supply increases. Do not increase
this resistance: it will increase ripple-current stress on the internal input-filter capacitor,
leading to early failure of the Model 8743-CL. The best strategy is to keep the resistance
between the power supply and the 8743-CL below 0.1 Ω and use the power supply
recommended by New Focus that came with the 8743-CL Controller/Driver.
3.5.1

Fault Protection

The 8743-CL Controller/Driver incorporates circuit-protection schemes to protect itself
and the system power supply:
Over-voltage protection: If the power input voltage exceeds 16.7 to 18.5 V, a transient
voltage suppressor (TVS) shunts the power input to ground. The internal 2.5 A fuse will
then open. The TVS will also shunt the power input to ground if an internal fault shorts
any high voltage to the power input. The input fuse will also open if the input power
voltage is reversed. Brief power supply transients will not blow the fuse. Therefore, it is
highly recommended to use the correct New Focus-supplied power supply. If the fuse was
blown, the unit has to be serviced by New Focus. It is not user replaceable.
Over-temperature protection: If the base plate of the unit reaches 80 °C, the unit will
turn the status indicator solid red to tell the user that the base plate, which acts as a
heatsink, reached the maximum allowed temperature. The user is expected to take some
measures like decreasing the pulse rate, force-air cool the 8743-CL case, or use an extra
heatsink. If the case temperature continues to rise, at 85 °C the output will be turned off.
The output will remain off until the base plate temperature decreases to 75 °C, when the
output will be ready to drive the motor again. In that case the status indicator will turn
solid green to indicate that the normal operation has resumed (see Table 1). If left
unattended, the unit will protect itself cycling between 85 °C and 75 °C.
The unit does not need an extra heatsink in normal laboratory environment. However, if
forced cooling is needed, usually at high ambient temperatures, a heatsink can be mounted
using the 4 slots of the unit base (see Figure 16).
31